An automatic transmission (AT) is a means for automatically shifting the gears of a vehicle. Most ATs in recent years combine, for example, a torque converter and a plurality of planetary gears and clutches. Because of automatic shifting with a plurality of clutches and the continuously variable shifting of the torque converter, there is no need for the driver to work the clutch upon starting, stopping, or shifting gears, as is necessary with a manual transmission (MT).
However, a torque converter transmits power through a fluid. Accordingly, the power transmission efficiency of an AT is lower than that of an MT, which transmits torque by direct mechanical linkage between the input and output sides. Therefore, an AT has the advantage of reduced fatigue on the driver, but has the drawback of higher fuel consumption for the vehicle.
In view of this, an automated manual transmission (AMT) has been proposed, which is based on the structure of an MT, and which affords the transmission efficiency of an MT while eliminating the need for clutch operation. More specifically, with an AMT, the clutch operation of an MT and the shifting operation of the transmission are automated. An AMT ensures the same transmission efficiency as a conventional MT, while eliminating the need for clutch operation.
However, with an AMT, during a shift the clutch is disengaged just as with an MT. so the transmission of torque is temporarily interrupted. While torque transmission is interrupted, the vehicle continues moving only by momentum, without accelerating. This torque cut-off greatly affects the acceleration performance of the vehicle, and also tends to produce a less comfortable ride for the driver. Meanwhile, with an AT, there is no torque cut-off during shifting because a plurality of clutches is used.
In view of this, it has been proposed that a multiple clutch device be employed as the clutch device of an AMT in order to solve this problem of torque cut-off (see, for example, Japanese Laid-Open Patent Application 2000-352431).